1. Technical Field of the Invention
The present invention relates to telephone networks and, in particular, to the common channel signalling links provided therein, and to the measurement of the message loads present on such signalling links.
2. Description of Related Art
Telephone networks utilize common channel signalling to facilitate message communications between the central processor in a parent exchange and the processors in any included regional equipment external to the exchange. Common channel signalling occurs over at least one of the communications links that also carry subscriber voice communications. At least one channel on at least one of the communications links is reserved for providing a two-way signalling path between the central processor and each of the regional equipment processors. A signalling terminal located at each end of the communications link functions to format processor signalling messages for transmission over the reserved channel, and further provides any other transfer control, maintenance or restart functions necessary for interfacing the link with the exchange and the regional equipment.
The processor signalling messages transmitted over the reserved channel of the communications link are formatted in accordance with the CCITT Common Channel Signalling System No. 7 level 2 protocol. These message transmissions comprise digital signals transmitted at a rate of 64 kbps. Analog message signals may also be transmitted in a common channel signalling system using the format defined by the CCITT Common Channel Signalling System No. 6 protocol at a rate of 2.4 kbps.
As the functional capabilities of telephone exchanges have improved to provide more and more services to subscribers, including the addition of so-called value added services, the demands placed on the reserved channel of the communications link in a common channel signalling system and the competition for access to and use of the communications link have increased dramatically. This is especially a concern in mobile telephone networks where the transmission capabilities of the communications links between the mobile service switching center of the exchange and the remote base stations which communicate with the cellular telephones dictate the number of signalling/transmission messages that may be handled by the network. Loading of the communications link, and in particular the common channel signalling system, adversely affects the nature and quality of the services provided to the subscribers. Accordingly, it has become increasingly important to monitor and identify in a graceful and progressive manner, and in real time, the load of useful traffic being serviced by the reserved channel on the communications link in a common channel signalling system.